Add string_view interface to from_chars

[mborland]

Closes: #143

[cppalliance-bot]

An automated preview of the documentation is available at https://147.charconv.prtest.cppalliance.org/libs/charconv/doc/html/index.html

[cppalliance-bot]

An automated preview of the documentation is available at https://147.charconv.prtest.cppalliance.org/libs/charconv/doc/html/index.html

[cppalliance-bot]

An automated preview of the documentation is available at https://147.charconv.prtest.cppalliance.org/libs/charconv/doc/html/index.html

[cppalliance-bot]

An automated preview of the documentation is available at https://147.charconv.prtest.cppalliance.org/libs/charconv/doc/html/index.html

[cppalliance-bot]

An automated preview of the documentation is available at https://147.charconv.prtest.cppalliance.org/libs/charconv/doc/html/index.html

[cppalliance-bot]

An automated preview of the documentation is available at https://147.charconv.prtest.cppalliance.org/libs/charconv/doc/html/index.html

[cppalliance-bot]

An automated preview of the documentation is available at https://147.charconv.prtest.cppalliance.org/libs/charconv/doc/html/index.html

[cppalliance-bot]

An automated preview of the documentation is available at https://147.charconv.prtest.cppalliance.org/libs/charconv/doc/html/index.html

[cppalliance-bot]

An automated preview of the documentation is available at https://147.charconv.prtest.cppalliance.org/libs/charconv/doc/html/index.html

[cppalliance-bot]

An automated preview of the documentation is available at https://147.charconv.prtest.cppalliance.org/libs/charconv/doc/html/index.html

[codecov]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (48b7098) 88.41% compared to head (aa93e3a) 88.52%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #147      +/-   ##
===========================================
+ Coverage    88.41%   88.52%   +0.10%     
===========================================
  Files           58       59       +1     
  Lines         7936     8032      +96     
===========================================
+ Hits          7017     7110      +93     
- Misses         919      922       +3     

Files	Coverage Δ
include/boost/charconv/detail/parser.hpp	79.79% <100.00%> (+1.55%)	⬆️
include/boost/charconv/from_chars.hpp	100.00% <100.00%> (ø)
test/from_chars_string_view.cpp	100.00% <100.00%> (ø)
test/limits.cpp	100.00% <100.00%> (ø)
test/roundtrip.cpp	98.42% <100.00%> (ø)
src/from_chars.cpp	90.00% <50.00%> (-10.00%)	⬇️

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 48b7098...aa93e3a. Read the comment docs.

[mborland]

@pdimov Do you see any issues with adding this interface? It seemed like a popular request on slack. The only thing I had a question about is can I tell the user to use boost::core::string_view since it's in a detail folder? I didn't want to use boost::string_view because it 1) adds another dependency and 2) does not have conversion from std::string_view.

[pdimov]

boost::core::string_view came about because we needed a string_view type that was convertible from and to std::string_view, but the maintainer of boost::string_view (Marshall Clow) refused to add such convertibility. So it's exactly what we need here.

It was originally a public part of Core, but people raised objections due to it duplicating the "real" boost::string_view, so I removed its documentation and moved it into a detail folder.

The current situation is not ideal, but we don't have any better ones. :-)